Synthetic polymeric materials such as polyacrylamides have long been used as flocculants in waste water treatment and other processes in which it is desirable to remove suspended solid materials. U.S. Pat. No. 3,235,490 discloses that certain crosslinked acrylamide based polymers are effective flocculants due to an electrostatic attraction followed by a sweeping action of a "filamentary" network provided by the crosslinked polymer. It is also disclosed that the formation of non-homogeneous products, which have a tendency to precipitate from solution, contributes to the effectiveness of the crosslinked polymers.
U.S. Pat. No. 4,720,346 describes a process for producing partially crosslinked acrylamide based cationic and anionic flocculants for use in municipal and industrial waste water treatment. The crosslinked polymeric material is said to have controlled non-linearity which is caused by crosslinking preformed polymers, or by polymerizing acrylamide monomers in the presence of a crosslinking agent. However, as disclosed therein, the intrinsic viscosity of the water soluble polymers decreases as the concentration of crosslinking agent is increased. Vigorous shearing action is required prior to or during flocculation to make the crosslinked or particulate polymeric material soluble and to increase the intrinsic viscosity. A high dosage of the polymeric material is required for effective removal of solids.
U.S. Pat. No. 4,759,856 describes a flocculation process for removing suspended solids in an aqueous suspension. A polymeric material comprising crosslinked water swellable polymer is added to water to form an aqueous composition, which is in turn added to an aqueous suspension for flocculation. The polymeric material must be subjected to shear during flocculation or in the aqueous composition before adding to the suspension.
Shearing or vigorous stirring of polymeric materials prior to or during flocculation requires process equipment which is often not available at the waste water treatment site. The additional shearing and stirring steps inevitably complicate the flocculent preparation, the flocculation process and reduce the cost efficiency.